Digestion of lignocellulosic materials with an organomercaptan and a hydrotrope



United States Patent 3 490,990 DIGESTION 0F LIGNOCELLULOSIC MATERIALSWITH AN ORGANOMERCAPTAN AND A HYDROTROPE Carl A. Johnson, Toledo, Ohio,assignor to Owens- Illinois, Inc., a corporation of Ohio No Drawing.Filed Dec. 30, 1966, Ser. No. 606,024 Int. Cl. D21c 3/20, 3/04 US. Cl.162-76 25 Claims ABSTRACT OF THE DISCLOSURE Methods of pulpinglignocellulosic material with an organomercaptan by digesting thelignocellulosic material with a treating liquor of an organomercaptanand a hydrotrope agent and continuing the digestion at a temperature andfor a period of time to convert the material to a treated material whichat least initially contains organomercaptan-reacted lignin.

This invention relates broadly to the art of treating lignocellulosicmaterials. More particularly it is concerned with such a treating orso-called pulping process wherein a lignin-reactive organomercaptan,e.g., thioglycolic acid (TGA) HSCH COOH, is employed in conjunction witha hydrotrope agent, that is, in a hydrotroping system, to cook or digestwood or other lignocellulosic material. The thioglycolic acid and/ orother organomercaptan are used under differing conditions whereby onecan obtain, merely by varying the treating conditions, chemicalcellulose, a moderate yield pulp (e.g., 60-69%) of good quality, or ahigh-yield pulp (e.g., 70-80%) as desired or as may be required by theparticular end-use. Surprisingly and unobviously the isolated ligninresulting as a by-product of the process is characterized by a formwhich is very similar to the orientation or configuration that lignin isbelieved to possess when it is in its natural or unisolated state in thewood.

In the usual overall process of pulping lignocellulosic material, e.g.,wood, the steps generally include 1) the initial step of treating thewood in chip or other subdivided form with a solvent to removeextractives and to leave a solid residue of lignin-holocellulose(lignocellulose); and (2) treating the resulting lignocellulose with asolvent that selectively dissolves lignin and leaves holocellulose (andusually also some lignin) as a solid residue or pulp.

The known pulping processes may be classified as:

(A) Mechanical pulping wherein separation of lignin from holocelluloseis eflFected by grinding to give mechanical pulp (groundwood) in high(90-95%) yield.

(B) Chemical pulping, which involves cooking the wood with highlyreactive inorganic chemicals to convert the lignin to water-solublederivatives containing such solubilizing groups as -ONa, SNa and SO Na.Typiv cal chemical processes are:

ice

(C) Semi-chemical pulping in which a first mechanical treatment and asecond chemical treatment are used.

(D) Bjorkman pulping and hydrotrope pulping wherein ligninsolubilization is achieved by a chemical treatment but without thechemical bonding of solubilizing groups to the lignin. In Bjorkmanpulping lignin is removed by milling the wood with toluene andextracting the residue with dioxane and water. In conventionalhydrotrope pulping, a salt, e.g., sodium xylene sulfonate (SXS), is used(specifically in the form of an aqueous solution) to increase theWater-solubility of the lignin. The nature of the salt-lignininteraction is unknown, but chemical bonding is not involved.

The treating or pulping method of the present invention falls into nosingle category or classification of the conventional pulping classessuch as those outlined above. In marked contrast it is a unique andunobvio-us combination of (1) a specific form of a chemical treatmentand (2) a conventional hydrotrope agent such as a solution of SXS and/ora hydrotrope-like agent, e.g., ethylene glycol and dimethylsulfoxide.For ease in description the term hydro-trope agent is used hereinspecifically as well as generically to include hydrotrope-like agentunless it is clear from the context that the latter meaning (namely, aspecific form of hydrotrope agent) is intended. By hydrotrope-like agentis meant a treating agent that performs the same function as aconventional hydrotrope agent in a wood-pulping process.

It was known prior to the present invention to pulp wood, specificallyspruce sawdust, by treatment with an organomercaptan, more particularlyTGA. See, for example, Ingeni-tirs Vetenskaps Akademien, Proceedings No.103, pp. (1930), The Mercaptans of Pine Wood, by Bror Holmberg.Holmbergs procedure was to treat, for instance, spruce sawdust with aTGA solution containing hydrochloric acid. In a second step themercaptanreacted lignin was extracted by treating the TGA-digested woodwith an aqueous solution of caustic soda, specifically at roomtemperature.

The present invention is based on my discovery that a hydrotrope systemcontaining an organomercaptan, e.g., (a) TGA; (b) a hydrotrope agent,e.g., SXS; and (0) water (when a. conventional hydrotrope agent, i.e.,one of the aqueous salt type is employed) provides a more specificdelignification process having a wider degree of flexibility as to theyield and character of pulp obtained than a system containing TGA, waterand hydrochloric acid.

In practicing the present invention any raw lignocellulosic material(that is, any wood or woody material, or mixtures thereof in anyproportions) may be cooked or digested with ingredients including anorganomercaptan and a hydrotrope agent, with or without first removingthe extractives by treating the lignocellulosic material in subdividedform (e.g., in the form of sawdust, shavings, wafers and/or chips) withan organic solvent capable of extracting the organic solvent-solublecomponents of the material. Such lignocellulosic materials includesoftwoods, hardwoods and fibrous annual plants. Examples of softwoodsare balsam fir, Eastern hemlock, jack pine, Eastern white pine, redpine, black spruce, red spruce, white spruce, tamarack and cypress.Examples of hardwoods are black gum, quaking aspen, mixed tomahawk,American beech, paper birch, yellow birch, Eastern cottonwood, sugarmaple, silver maple, yellow poplar, black cherry and white oak. Examplesof fibrous annual plants are bagasse, hemp and jute. Mixtures of woodsor other lignocellulosic materials of diiferent origin may be used ifdesired, e.g., mixtures of different softwoods, or of differenthardwoods, or of one or more softwoods and one or more hardwoods.

THE ORGANOMERCAPTAN REACTANT Illustrative examples of organomercaptansthat may be used in conjunction with a hydrotrope agent in digestingwood in accordance with this invention are those embraced by the generalformula wherein R represents a divalent radical, more particularly adivalent hydrocarbon radical, Y represents a monovalent substituentbonded directly to R, and n represents a numeral ranging from up to thecombining power (i.e., a value that will completely satisfy allvalences) of the divalent radical represented by R.

Illustrative examples of divalent radicals represented by R in Formula Iare divalent hydrocarbon radicals and, more particularly, divalentaliphatic, especially divalent saturated aliphatic, e.-g., ethylene,propylene (trimethylene), butylene, isobutylene, pentylene,isopentylene, decylene, etc., including divalent cycloaliphatic,especially divalent saturated cycloaliphatic, e.g., cyclopentylene,cyclohexylene, cyclohepthylene, etc.; divalent aromatic, e.g.,phenylene, naphthylene, etc.; divalent aliphatic-substituted aromatic,e.g., 2,4-tolylene, ethyl 2,5 phenylene, isopropyl 3,4 phenylene, 1butyl 2,4 napthylene, etc.; divalent aromatic-substituted aliphatic,e.g., phenylethylene, phenylpropylene, naphthylisobutylene, xylylene,etc.; and radicals that may be classed either as divalentaromatic-substituted aliphatic or divalent aliphatic-substitutedaromatic, e.g., 4-,alpha-tolylene, 3, betaphenyleneethyl, 4,alphaxylene, 2,gamma phenylenebutyl. etc. Thus R may represent a divalenthydrocarbon radical represented by the general formula where Arrepresents an arylene radical and R represents an alkylene radical.Preferably the divalent hydrocarbon radical represented by R containsnot more than carbon atoms, more particularly from 1 to 8 carbon atoms.

Preferably, also, the divalent radical represented by R in Formula I isfree from olefinic or acetylenic unsaturation either in a straight chainor in a side chain.

It is not essential that the divalent radical represented by R becomposed solely of carbon and hydrogen atoms. For example, the chain ofcarbon atoms, whether straightchain aliphatic or carbocyclic, may beinterrupted in the chain by other atoms, e.g., by oxygen and/or sulfurand/ or nitrogen atoms bonded directly to carbon atoms of the chain.

Illustrative examples of substitutents represented by Y in Formula I arefunctional groups such as OH; -CN; SH; COOH; -COOR', wherein R is amonovalent hydrocarbon radical corresponding to the divalent hydrocarbonradicals represented by R in Formula II; COOM, wherein M is asalt-forming cation, e.g., N I-I or Na, K, Li or other alkali metal, asalt-forming amine such as a mono-, di-, ortri-(hydrocarbon-substituted) or -(hydroxyhydrocarbon-substituted)amine, or other salt-forming cation and especially those which yieldwatersoluble salts when present in the particular thio compound. Or, Ymay be radical represented by wherein R" and R' are members of the groupconsisting of hydrogen and monovalent hydrocarbon radicals correspondingto the divalent hydrocarbon radicals represented by R in Formula I.

4 It will be understood, of course, by those skilled in the art thatwhen n in Formula I represents zero (0), then there are no radicalsrepresented by Y in the formula which latter then becomes (III) HSRwherein R represents a monovalent radical, more particularly amonovalent hydrocarbon radical corresponding to the divalent hydrocarbonradicals represented by R in Formula I. Illustrative examples ofmercapto compounds embraced by Formula III are the alkyl (includingcycloalkyl), aralkyl, aryl and alkaryl mercaptans, more particularlythose which contain from 1 through 10 carbon atoms and especially thosehaving not more than about 8 carbon atoms.

The relatively low water-solubility of the unsubstituted hydrocarbylmercaptans embraced by Formula III makes them much less suitable for usethan substituted hydrocarbyl mercaptans having one or more polar orsolvating substituent groups. However, if water-solubility of themercapto reactant is unimportant, e.g., when it is to be used inundiluted state, or in solution in an organic solvent (e.g., ethanol) orin a mixture of water and an organic solvent in which mixture theunsubstituted hydrocarbyl mercaptan is adequately soluble, then amercaptan within the scope of Formula III may be employed as a treatingagent.

Particularly useful in practicing the present invention areorganomercaptans represented by the general formula wherein Z representsan alkylene (including cycloalkylene) radical containing from 1 through10 and preferably from 1 through about 8, carbon atoms; R represents amember of the group consisting of (a) hydrogen, (b) alkyl radicalscontaining not more than about 10 carbon atoms and preferably a loweralkyl radical (e.g., an alkyl radical containing from 1 through about 6carbon atoms); and (c) a salt-forming cation, examples of which havebeen given hereinbefore with reference to M in the grouping COOM whichmay be a substituent represented by Y in Formula I; and n represents aninteger from 1 up to that of the combining power of the alkylene radicalrepresented by Z. The alkylene radical represented by Z may bestraight-chain, branchedchain or cyclic as in, for example, cyclopentyl,cyclohexyl and the like.

More specific examples of mercapto compounds embraced by Formula IV aremonocarboxylic and polycarboxylic acids such as those having theformulas (v1) HSCHCH2-COOII coon (v11) ns-cn-c o 011 (VIII) sumo-coon(IX) rrs-o oHn-cHT-c 0 on (x) ns-cn-co on Hr-COOH wherein n representsan integer from 1 to 6, inclusive, more particularly from 1 to 4,inclusive, and R has the same meaning as given above with reference toFormula IV. Thus, compounds embraced by Formula XI may be the thio aciditself or a salt (especially a water-soluble salt) or an ester of suchan acid. Of these compounds thioglycolic acid and the water-solublesalts and the lower alkyl esters thereof are the more preferredsub-group. Mixtures of acids and/or salts and/0r esters embraced byFormula XI may be used if desired.

Instead of using organomercaptan compounds that are within the scope ofFormula XI, one may employ those wherein the -COOR group in that formulahas been replaced by other hydrolyzable or solvating groups such whereinR" and R' in the last two groups are hydrogen or a monovalenthydrocarbon radical corresponding to one of the divalent hydrocarbonradicals represented by R in Formula I.

THE HYDROTROPE AGENT Conventional hydrotrope agents (hydrotropicsolutions) have been defined as those aqueous salt solutions whicheffect decidedly greater solubility of slightly soluble substances thandoes pure water at the same temperature [referencez McKee, Use ofHydrotropic Solutions in Industry, Ind. and Eng. Chem., 38, 4 (1946)].McKee describes this phenomenon as being the reverse of the commonsalting-out effect following the addition of many electrolytes toaqueous solutions of numerous solutes This salting-in, as opposed tosalting-out, effect is best shown by concentrated aqueous solutions ofvery soluble salts of organic acids, with organic substances as soluteswhich have a low solubility in water Typical of these hydrotropic saltsare the alkali or alkaline earth salts of the sulfonates of toluene,xylene, or cymene, the alkali benzoates, thiocyanates, and salicylates,and, for some compounds (particularly inorganic), even such common saltsas the alkali bicarbonates, oxalates, and thiocyanates.

Among the conventional hydrotrope agents that are particularly useful incarrying the present invention into effect are the alkali-metal salts,especially the sodium salt, of xylene-sulfonic, cymenesulfonic andbenzoic acids; and, of these, the sodium salt of xylenesulfonic acid ispreferred.

Illustrative examples of hydrotrope-like agents, in addition to theaforementioned ethylene glycol and dimethylsulfoxide, that may beemployed are: n-hexyl Cellosolve (ethylene glycol mono-n-hexyl ether),n-hexyl Carbitol (diethylene glycol mono-n-hexyl ether), di-n-butylCarbitol [bis(beta-n-butoxyethyl) ether], isophorone, n-butanol,Z-ethylhexanol, pyridine, dimethyl-formamide and dimethylacetamide.

Instead of using a single conventional hydrotrope agent, one may employa plurality (2, 3, etc.) of such agents; or a plurality ofhydrotrope-like agents in place of only a single such agent; or amixture of one or more conventional hydrotrope agents and one or morehydrotrope-like agents in any proportions.

The hydrotrope-like agents, numerous examples of which have been givenhereinbefore, are not the full equivalent of conventional hydrotropeagents, e.g., sodium xylene sulfonate (used in the form of an aqueoussolution), in practicing the present invention.

6 TREATMENT OF RAW LIGNOCELLULOS IC MATE- RIAL WITH A COMBINATION OF ANORGAN- OMERCIAPTAN AND A HYDROTROPE AGENT The treatment of rawlignocellulosic material with an organomercaptan is described in, forexample, the aforementioned Holmberg publication. Other methods oftreating wood and other lignocellulosic materials with anorganomercaptan are described in, for instance, the copend ingapplication of William E. Fisher and Shibley A. Hider, Ser. No. 605,978,filed concurrently herewith, assigned to the same assignee as thepresent invention, and which by this cross-reference is made a part ofthe disclosure of the instant application.

The treating liquor used in practicing this invention contains areactive agent comprised of at least one organomercaptan, preferably TGAand/or a water-soluble salt thereof, dissolved or dispersed in a liquidreaction medium comprised or consisting essentially of a hydrotropeagent. The concentration of the organomercaptan in the aforesaid liquidreaction medium cannot be stated with precision since it is dependentupon so many different influencing factors including, for example, thekind of wood or other lignocellulosic material being digested; thenature of its subdivided form; the ratio between the organomercaptan andthe lignocellulose; the temperature and pressure of digestion; type ofdigester employed; and other influencing factors. Generally, however,the organomercaptan constitutes, by weight, from about 1% to about 14%,more particularly from about 2% to about 6%, of the weight of the liquidreaction medium containing the hydrotrope agent.

The digestion may be carried out (or initiated and then continued) underacid, neutral or alkaline conditions. Thus, the treating liquor duringthe period of digestion may vary within the pH range of from about 2.0to 14.0; or the liquor may have an alkalinity greater than a pH of 14.0,in which case the alkalinity may be expressed in terms of the percentageof the particular basic substance in the liquor or in any other suitableterms.

The alkalinity of the treating liquor is adjusted to the desired levelby adding any suitable acid or base in the amount required to attain thedesired level if it is not already at that point. Thus one may use suchinorganic acids as, for example, hydrochloric, sulfuric, sulfurous orphosphoric acids; or organic acids such as benzoic acid, benzenesulfonicacid, toluenesulfonic acid, xylenesulfonic acid, cymenesulfonic acid, ora chloroacetic acid including diand trichloroacetic acids. Or, whenrequired, one may employ for alkalinity-control (specificallypH-control) purposes an alkali-metal hydroxide, preferably sodiumhydroxide, or other suitable inorganic base.

Chemical treatment of raw lignocellulosic material with a treatingliquor comprising an organomercaptan and a hydrotrope agent may beeffected at a temperature within the range of, for instance, from 70 C.(preferably at least about 100 C.) to 200 C., more particularly fromabout to 190 C., and still more particularly at from about -180 C. Thetime of treatment varies, for example, from A2 to usually 4 or 5 hoursbut which sometimes may be 6 or 8 hours or more. This time period andthe reaction temperature depend upon such influencing factors as, forinstance, the type and degree of sub-division of the lignocellulosicmaterial being treated, the chosen organomercaptan and hydrotrope agent,the amount and concentration of the organomercaptan compound, whether ornot the initial digestion period is to be followed by a secondextraction-stage whereby lignin is extracted from the Wood, the type ofproduct desired, the type and size of digester used, and otherinfluencing factors.

The concentration of organomercaptan, e.g., TGA, in the treating liquorwith respect to the oven-dried (O.D.) lignocellulosic material should beat least about 5% by weight thereof. Thus, it may be, for example, fromabout 5% to about 100%, more particularly from about 10% to about 50%,by weight of the OD. lignocellulosic material charged to the digester.

The organomercaptan component (i.e., a single organomercaptan or aplurality of different organomercaptans) may be the only reactive agentused in conjunction with a hydrotrope agent to constitute the treatingliquor; or, the said organomercaptan component may be employed in theform of an admixture with a minor amount (less than 50% by weight of theadmixture) of an inorganic thio reactant, e.g., sodium sulfhydrate(NaSH), sodium sulfide, sodium polysulfide, etc.

One of the advantages of the method of the instant invention is theflexibility with which it lends itself to the obtainment of highormoderate-yield pulps or alphacellulose merely by changing such operatingparameters as pH, time and temperature of digestion, and amount of TGAand/or other organomercaptan employed. Furthermore, the method makespossible the recovery of a relatively high proportion of the organicmaterial that is left in the treating liquor.

In other words, the operating parameters can be varied to obtain ligninand/or pulp or cellulose residue having the desired properties. Theconditions can be varied to produce pulp (hence also paper) having awide range of physical properties; and, additionally, a recoverablelignin having a wide range of utility. For example, the recovered lignincan be utilized as a thermosetting resin, as a coating material or as acomponent of coating compositions, as a starting material for makingchemical compounds and various chemical compositions, and for many otherpurposes.

Surprisingly it was found that the organomercaptanreacted lignin notonly can be readily separated from the wood, thereby permitting easierdefibration of the wood chips; but also that the isolated ligninderivatives can be hydrolyzed in an alkaline ethylene glycol mediumwhereby there is obtained a higher percentage of water-soluble materialof lower molecular weight than heretofore could be obtained byconventional pulping processes. In other words, the method of thisinvention makes it possible to isolate lignin polymer in a non-condensedstate such that it is amenable to controlled hydrolysis to smallerunits. Thus, the present invention provides a pulping technique wherebythe lignin polymeric material is protected or prevented from reactingwith itself during its isolation and under conditions that yield a goodgrade of pulp.

It has been indicated hereinbefore that the initial digestion period maybe followed by a second extraction stage whereby lignin is extractedfrom the wood. Whether or not a one-stage or a two-stage pulpingtechnique is carried out depends mainly upon such influencing factors asthe pH of the treating liquor, the time and temperature of the reaction(especially the temperature), and the type of product desired, e.g.,alpha-cellulose, or a moderateor high-yield pulp best adapted for theparticular end-use. Highly alkaline cooks (i.e., when the digestion isinitiated at a pH not less than 11.0) at higher temperatures, e.g.,120-200 C., generally may be efnployed when it is desired to effectpulping in a single stage. Cooks may be carried out at an acidic pH,e.g., at a pH of from about 2.0 to about 4.0 or 5.0, and at atemperature substantially above 100 C., e.g., about 120-200 C. Suchoperating parameters may be employed when, for example, as under theaforementioned highly alkaline conditions, it is desired to provide aonestage pulping method wherein the organomercaptanreacted lignindissolves in the liquid reaction medium more particularly in a liquidhydrotrope agent consisting essentially of a concentrated aqueoussolution of a very water-soluble salt of an organic acid, andspecifically SXS.

Cooks also may be carried out, as indicated in one of the examples thatfollows, under neutral or approximately neutral conditions (e.g., at apH of from about 6.5 to about 7.5) and at temperatures of from 80 to 200C.

When the raw lignocellulosic material has been elfectively digested orpulped in a one-stage technique, the charge is blown or otherwiseremoved from the react r into a suitable draining or filtering unit,e.g., a wash pit, wherein the liquor is removed from the solid product.The resulting fibrous pulp is washed free of liquor, e.g., with hotwater, and screened. Bleaching and/or drying steps are optionaldepending upon the end-use. If bleaching is to be effected, it isusually done before dying of the pulp. If the raw lignocellulosicmaterial has been cooked under strongly alkaline conditions then, priorto the bleaching step, the crude pulp may be washed With a diluteaqueous solution of an inorganic acid, e.g., a 5% aqueous HCl solution,thereby to insure a more complete and eflicient bleaching action thanwhen bleaching is effected in the absence of such a dilute acid wash.The pulp, with or without further treatment as maybe required for theparticular end-use, is then suitable for utilization in making anydesired cellulosic product including, for example, paper and relatedproducts, cellulose acetate, cellulose xanthate, regenerated cellulose,ethyl cellulose, etc.

TWO-STAGE PROCESS In a two-stage process the excess liquor is preferablyremoved (e.g., by draining) from the reactor or digester at the end ofthe cooking period, and the residue is washed, e.g., with hot water.

The washed, subdivided wood containing organomercaptan-reacted lignin isthen either transferred to an extraction vessel, the type of which willvary with the particular extraction conditions that are deemed necessaryor advisable; or the digester in which the initial cooking was carriedout may be used as the extraction vessel.

Organomercaptan-reacted lignin retained by the washed residue isextracted by contacting the said residue with an organic or inorganicextractive agent for the said lignin thereby to form a cellulosic pulp.This extractive agent may be an extractive amidogen compound, e.g., anamine such as monoethanolamine, aniline, and the like; or an amide,e.g., urea, dimethylformamide, etc. Or, the extractive agent may be asolution (including dispersion), preferably an aqueous solution of aninorganic base, e.g., an aqueous solution containing from Arm 4 or 5weight percent of sodium hydroxide or of a hydroxide of any other alkalimetal or of an alkaline-earth metal.

Crude commercial mixtures of amidogen compounds, e.g., mixtures ofamines may be used, if desired, as the lignin-extracting agent. Alkalineinorganic agents, e.g., NaOI-I, Na CO Na s, NaSH, etc., may be employed,if desired, in combination with an amine or other nitrogenousextractant.

In extracting the organomercaptan-reacted lignin from the rawlignocellulosic material that has been digested with a treating liquorof the kind used in practicing this invention, the extractiontemperatures may range, for instance, from ambient temperature (about2030 C.) to about 200 C., more particularly from about 50 .or C. toabout 180 C., while the extraction time may range, for example, fromabout A to about 4 or 5 hours or longer, as desired or as conditions mayrequire. Thus, the extraction temperature and time may be -170 C. forfrom 1 to 2 hours, more particularly when the extractant is a diluteaqueous solution of sodium hydroxide containing, for example, from about1 to about 2 weight percent of NaOH.

Several examples of extractive amidogen compounds that may be employed(singly or a plurality thereof) as an extractant of theorganomercaptan-reacted lignin have been given hereinbefore. Otherexamples of such amidogen compounds of the amide type include thiourea,diurea, diethylenetriurea, methylurea, phenylthiourea, asymmetricaldiethylurea, guanidine, dicyandiarnide, guanylurea, guanylthiourea,biguanide, monophenylbiguanidine, l-aminoguanidine (guanylhydrazine),and the like.

Still other examples of extractive amidogen compounds that may be usedinclude:

The mono-, diand trimethylthrough -dodecylamines (both normal andisomeric forms) wherein the secondary and tertiary amines are eithersymmetrical or unsymmetrical, e.g., N-ethyl-N-butylamine.

The mono, diand triphenylamines, the mono-, diand tritolylamines, themono-, diand tribenzylamines, the mono-, diand tri(cyclohexyl)amines,and wherein the secondary and tertiary amines are either symmetrical orunsymmetrical.

The diand triethanolamines, the mono-, diand trin-propanoland-isoprpanolarnines and higher members of the homologous series, whereinthe secondary and tertiary amines are either symmetrical orunsymmetrical.

Amines such as 2 amino 4 methylpentane [CH CHNH CH CH(CH3)2] and3-amino-5-methylpentane.

The alkylenepolyamines (polyaminoalkanes), e.g., Ethylenediamine(1,2,-ethanediamine) 1,2-diaminopropane (propylenediamine)1,3-diaminopropane (NH CH CH CH NH 3-diethylaminopropylamine (C H NCH CHCH NH 1,3-diaminobutane (NH CH CH CHNH CH 1,3 bis ethylaminobutane [C HNHCH CH CHNH- 2 5) 3l 1,4-diaminobutane 1,5-diaminopentane1,6-diaminohexane 1,7-diaminoheptane 1,8-diaminooctaneDiethylenetriamine (NH CH CH NHCH CH NH Triethylenetetramine v [-NH (CHCH NH CH CH NH Tetraethylenepentamine Pentaethylenehexamine temperature,or it may be employed in the form of a' solvent solution thereof, e.g.,dissolved in water and/or methanol, ethanol, isopropanol or other loweralkanol and/ or other organic solvent for the said extractant.

Certain organic solvents free from an organic or inorganic base of thekind hereinbefore described also may be used to extract theorganomercaptan-reacted lignin from the treated lignocellulosicmaterial. Examples of such solvents are dimethylsulfoxide and ethyleneglycol, both of which, however, are not as effective extractants asmonoethanolamine; and dioxane, which is much less effective thanethylene glycol, dimethylsulfoxide and monoethanolamine, but moreeffective than pyridine and N,N-dimethylacetamide under the sameextraction conditions.

Organic solvent-type extractants containing a dissolved or dispersedorganic or inorganic base also may be used as the extractant.

Extractions may be carried out under reflux conditions, or they may beeffected under superatmospheric pressure sufficient to liquify theextractant (e.g., an amidogen compound of the low-boiling amine type) ifOtherwise it would be in gaseous state at the extraction temperature.

At the end of the extraction period the residue or pulp is treated toremove the organic or inorganic extractant containingorganomercaptan-reacted lignin. For example, the residue or pulp may bedrained and screened to separate the solids which are then defibratedand washed with water or other suitable solvent. When the extractant is,for instance, a water-soluble amidogen compound such as a water-solubleamine, or a water-soluble inorganic base such as sodium or otheralkali-metal hydroxide, the solid residue is advantageously washed withhot water. With extractive amidogen compounds such as aniline,substantially pure aniline itself may be used as the washing agent; or adifferent organic solvent, preferably a water-soluble organic solvent,e.g., methanol, ethanol or dioxane, may be employed. The recoveredextraction liquors and washings may be either concentrated, ifnecessary, and reused in the process; or, they may be treated to recovervaluable organomercaptanreacted lignin and to purify the unreactedextractant. Only a small amount of the extraction agent is consumed inthe extraction, and the extraction liquor may be repeatedly recycled inthe process before any losses need to be replaced. Any ligneous materialthat precipitates may be removed by any suitable means, e.g., byfiltration.

In purifying the extraction agent and recovering the mercaptan-reactedlignin, the extraction liquor may be treated with, for example, CO or adilute mineral acid such as HCl; an inorganic salt; or anextractant-compatible liquid in which the lignin is insoluble, e.g.,alcohol, in order to precipitate the ligneous material for recovery.Dialysis also may be employed to separate the lignin from the extractionliquor. Or, the liquor containing the dissolved lignin may be passedthrough an anion-exchange resin in free-base form thereby selectively toadsorb on the resin anionic materials contained in the liquor while thelignin in purified form passes through the resin for subsequentevaporation of the eluate and recovery of lignin. This latter techniqueis more fully described and broadly and specifically claimed in thecopending application of William H. Greive and Karel F. Sporek, Ser. No.418,872, filed Dec. 16, 1964, now abandoned and assigned to the sameassignee as the present invention.

If the extractant is a volatile amidogen compound with a relativelylow-boiling point, it may be recovered by distillation from thelignin-containing liquor in which it is present and reused in theprocess. Higher boiling extractive amidogen compounds may be recoveredfrom this liquor by extraction with low-boiling solvents. Afterdistilling off the low-boiling solvent, bleaching and/or drying steps,as well as acidification to insure a more efiicient bleaching action,may be carried out as previously has been described with reference tothe one-stage process.

In order that those skilled in the art may better understand how thepresent invention can be carried into effect, the following examples aregiven by way of illustration and not by way of limitation. All parts andpercentages are by weight unless Otherwise stated.

EXAMPLE 1 This example illustrates the digestion under acidic conditionsof a softwood, specifically isopropanol-extracted cypress, in a treatingliquor comprising an organomercaptan, more particularly TGA, and ahydrotrope agent, specifically a concentrated (about 36%) aqueoussolutionof SXS.

The procedure employed'to'extract the cypress in chip form involves avapor extraction of the chips with a reboiler wherein the extractivesare accumulated and the solvent, isopropanol, is flashed off.Isopropanol (about 1.5 liters) is employed to extract 1 kg. of cypresschips. (The same apparatus and procedures are used in removingextractives from chips of pine, green aspen, and other woods which areprocessed in practicing the present invention.)

In a specific pulping procedure a total of 300 g. (ovendry basis) ofisopropanol-extracted cypress chips is added to a 2100 ml. watersolution in a 3-liter reaction kettle. This water solution contains (a)36% sodium xylene 11 sulfonate (SXS), (b) 300 g. thioglycolic acid (TGA)and (c) a concentration of 1.8 N p-toluenesulfonic acid 12 CorrectedD.P. values given in the table are calculated on the assumption that nolignin goes into solution.

TABLE I.PULPING OF ISOPROPANOL-EXTRACTED CYPRESS CHIPS Pulp Time, PulpKlason Corrected No. hours 'lemp., 0. 11+ TGA 1 yield lignin P.P. D.P

1-A 4. 102 l. 8 N 100 42. 7 0. 8 289 286 l-B- 4. 0 90 l. 8 N 50 55. 1 9.9 370 335 1-0. 2.0 92 1. 8 N 100 57. 7 10. 6 383 344 1-D 4. 0 101 0. 9 N50 52. 0 7. 6 397 367 1E 2.0 101 0.9 N 100 65. 4 13. 6 414 361 1-F. 2.090 0.9 N 50 71. 7 28. 1 1-G- 4. 0 92 0. 9 N 100 47. 1 4. 8 305 291 1H 2.0 102 1. 8 N 50 57. 0 12. 4 383 340 1 TGA in approximately a 36% aqueoussolution of SXS.

EXAMPLE 2 Same as in Example 1 with the exception that the wood which ispulped is a hardwood, specifically black gum chips.

The details of the operating parameters for the individual runs,together with the pulp yields, Klason lignin values, and corrected anduncorrected D.P. values of the pulp are given in Table II.

TABLE II.-PULPING OF ISOPROPANOL-EXTRACTED BLACK GUM CHIPS.

Pulp Time, Pulp Klason Corrected No. hours Temp, 0. 11+ TGA 1 yieldlignin P.P. D.P

4. O 103 1. 8 N 100 43. 5 0. 6 279 276 4. 0 90 1. 8 N 50 45. 9 1. 8 433424 2. 0 103 0. 9 N 100 45. 4 l. 8 459 449 4. 0 102 0. 9 N 50 43. 5 0. 8410 407 2. 0 91 l. 8 N 100 44. 3 5. 1 456 433 2. 0 90 0. 9 N 50 49. 610. 6 354 318 4. 0 91 0. 9 N 100 50. 3 4. 0 462 443 I TGA inapproximately a 36% aqueous solution of SXS.

30 C.). The chips defibrate into a fine, white pulp.

The white pulp is filtered off from the brown liquor, and 40 washed withwater until neutral to litmus paper. The yield of pulp is 51%; Klasonlignin value, 6%. (The Klason lignin value is determined as describedin, for example, TAPPI Standard Test Method T13 m54.)

EXAMPLE 3 Same as in Example 1 with the exception that a differentsoftwood is employed, specifically chips of Valdosta pine.

The details of the operating parameters for the individual runs,together with the pulp yields, Klason lignin In a manner similar to thatdescribed in the preceding values, and corrected and uncorrected D.P.values are paragraph, four variables in the operating parameters aregiven in Table III.

TABLE I.-IULPING OF ISOPROPANOL-EXTRAOTED VILDOS'IA PINE CHIPS Time,Pulp Klason Corrected hours Temp., 0. 11+ TGA 1 yield lignin P.1. D.P

4. 0 103 1. 8 N 100 42. 6 0. 4 346 343 2. 0 103 1. 8 N 47. 0 3. 0 436425 4. 0 102 0. 9 N 50 46. 1 8. 4 482 464 2. 0 102 0. 9 N 100 51. 1 4. 2466 446 4. 0 91 0. 9 N 100 56. 7 10. 3 403 364 2. 0 90 1. 8 N 100 58. 311. 5 485 432 4. 0 89 1. 8 N 50 50. 0 10. O 479 436 2. O 90 0. 9 N 5060. 5 18. 6 219 181 1 TGA in approximately a 36% aqueous solution ofSXS.

are run at two levels. A constant liquor level of 700 ml. is

used in each run. The variables and levels are as follows:

EXAMPLE 4 Same as in Example 1 with the exception that two A B differentconditions are employed and, before digestion, 1. Hydrolysis time, hours4 the yp ip re soaked for av prolonged period, 2. YdrolySiS t p i 1 ,Q-(DD J specifically 66 hours, in the treating liquor at ambient fit r lilfif"???it???31????33???. 0 9 N 1 8 N temperature (about 2040 C.). TGAconcentration 100 chips 50 100 The details of the operating parametersfor each run,

The details of the operating parameters for the individual runs,together with the pulp yields, Klason lignin values and corrected anduncorrected D.P. (degree of polymerization) values of the pulp are givenin Table I.

The uncorrected D.P. value of the pulp is determined as described inSCAN-C15z62 (Scandinavian Pulp, Paper together with the pulp yields andKlason lignin values, are given in Table IV. For ease of comparisonthere is 70 included in this table the corresponding data on pulp Nos.l-B and l-E from Table I. It will be noted that in each case there was alowering of the pulp yield and of the Klason lignin content by the66-hour presoaking and Board Testing Committee), Tables 1-3 and 7. Thetreatment in the treating liquor.

' Ethylene glycol.

TABLEIV.-HOTPULPINGOFISOPROPANOL-EXTRACTED CHIPS AFTER SOAKING FOR 66HOURS AT AMBIENT TEMPERATURE EXAMPLE This example illustrates therelative effectiveness of various organic solvents as extractants oforganomercaptan-reacted lignin' from black gum wood chips that have beendigested under acidic (PTSA) conditions in a treating liquor comprisingTGA in approximately a 36% aqueous solution of SXS. The operatingparameters for the digestion correspond to those given for pulp No. 2-AinTable-II.

The organic solvents tested include monoethanolamine (MEA),dimethylsulfoxide, ethylene glycol, dioxane, pyridine and'N,N-dimethylacetamide. The black gum chips (50 g., O.D. basis) arerefluxed in about 300 ml. of the solvent for 2%. hours, mechanicallystirred to de fiber the chips in fresh solvent at ambient temperature,filtered, and washed with fresh solvent at room temperature for 5minutes. The filtered pulps are suspended in a blender With water toremove the solvent employed in the individual run.

Below are shown the reflux temperatures of extraction with each solvent,and the percent of Klason lignin in the extracted pulp.

Refiux temper- Percent Klason E xtraction Solvent ligninMonoethanolamine Dimethylsulfoxide.

Dioxane ridlne N, -dimethylaceta.mide

' Another run is made, as described above, using monoethanolamine as anextractant but limiting the reflux time to one hour. "The resulting pulpis white, and con- EXAMPLE 6 The same general procedure is followed asdescribed in the third paragraph of Example 1 with the followingexceptions:

Three large digestions or cooks using" 300 g. of isopropanol-extractedO.D. cypress chips are run at reflux 14 chips are extracted withmonoethanolamine at reflux temperature (129*133 0).

Similar two-hour cooks at 100 C. are also madeon isopropanol-extractedcypress and approximately a 50/50 by weight mixture ofisopropanol-extracted cypress and isopropanol-extracted black gum. Thechips are cooked in the same formulation of treating liquor describedabove. Lignin is extracted from the digested chips by treatment with a4% aqueous solution of NaOH at room temperature.

Details of the pulping conditions for the individual runs, and yieldsand properties of the pulps are given in Table V-a. Also shown in thistable are the percent pulp yields and percent Klason lignin contents ofpulps resulting from simulated kraft cooks of cypress and of pine in anautoclave. The cook formulation and cooking procedure employed in makingthese kraft cooks are given below. The cooks differed only as to thetype of wood used; that is, cypress chips were employed to obtain PulpNo. V-F, and pine chips in making Pulp No. V-G.

(I) Cook formulation Chip charge: 150.0 g. (O.D. weight) of air-driedchips;

pre-extracted with 1:2 alcoholbenzene Liquor composition: 14.4 g.p.l. NaCO (7.6% as Na O on the OD. wood); 41.9 g.p.l. NaOH (29.3% as Na O onthe OD. wood); 18.4 g.p.l. Na s (13.1% as Na O on the OD. wood) Liquoractive alkali as Na O: 47.1 g.p.l. (42.4% on the OD. wood) Liquor totalalkali as Na Oz 55.5 g.p.l. (50.0% on the OD. wood) Liquor sulfidity:26.3% of the total alkali Liquor-to-wood ratio: 9: 1

Total liquor volume: 1350 ml.

The above liquor was prepared by dilution of concentrated mill Whiteliquor. The active alkali concentration of 47.1 g.p.l. as Na O is thesame as that of a mill cook at 16% active alkali on the wood and 3.4liquor-to- Wood ratio. As a result of the high liquo'r-to-wood ratiorequired in these cooks (9:1), the active alkali on the wood was at ahigh level (42.4%) compared to mill pulping.

(II) Cooking procedure The charge of chips and liquor was cooked withstirring in a stainless steel, electrically heated and Water cooled,one-gallon autoclave under the following condition-s:

Max. cook temperature: 338 F. (170 C.) Time at temp. (338 F.): 26 min.

Time to temp. (338 F.) min.

Cooling time to F.: 25 min.

The resultant digested wood was recovered by filtration, then washedthoroughly with hot water. After defibering the cooked Wood in aSprout-Waldron refiner, the pulp was refined and paper sheets Were madefor testing.

Table V-a follows.

TABLE Va.PULPIN'G CONDITIONS, YIELDS AND PROPERTIES OF PULPS FROMTGA-SXS COOKS Time, Temp., Yield, K.L., Corrected Wood hrs. 0.Extraction treatment percent percent D. P D. Pfl

2 100 15 Ext. in RT 1 aqueous N aOH 51. 3 5. 96

2 102 1 hr. Ext. in 131 C. MEA, 45. 5 2. 32 288 295 1% 100 1 hr. Ext. in133 C. MEA 50.0 3. 47 331 341 101 1 hr. Ext. in 129 C. MEA. 51. 8 3. 35426 440 1 R.I.= Room temperature (about 25-30 0.).

2 K.L.=Klason lignin (reL: TAPPI Standard T13 m-54). 3 D.P.=Degree ofpolymerization.

4 Simulated standard Kraft cook in autoclave.

(III) Refining, sheetm-aking and testing The procedures used in thesesteps were essentially the same as those described in the aforementionedFisher et :al. copending application Ser. No. 605,978 with the followingexception. In the case of Pulp Nos. V-F and V-G only one refining waspossible because of the small amount of pulp obtained from the cooks.Only one refining also was carried in the production of the other pulps.Additional details on refining technique, and sheetmaking and testing ofthe handsheets, follow:

The wet cellulosic pulp produced as hereinbefore described was dried to20-30% solids. A portion, based on the OD. weight of the wet pulp, wasrefined with water at 1% consistency in a Mead Laboratory Refiner(manufactured by The Bauer Bros. Company, Springfield, Ohio). The degreeto which the pulp was refined, as determined by measuring the dnainagetime (TAPPI Standard T221) of the pulp in a Slowness Tester(manufactured by Williams Apparatus Company, Watertown, N.Y.), wascontrolled so as to refine, as closely as possible, to a WilliamsSlowness of 55 seconds.

The handsheets were formed in an 8" x 8" Williams sheet mold fromaliquots of the pulp slurry that were measured volumetnically so as toobtain sheets corresponding as nearly as possible to 2'6 lb./MS-Fsheets, i.e., 4.6 grams of O.D pulp per sheet. The pulp consistency onforming the sheets was adjusted to 0.05% by further dilution of the pulpaliquot in the mold. The seven or more sheets (wet webs) formed fromeach batch of pulp slurry were couched from the wire of the mold ontostandard 12" x 12'' TAPPI blotters, then stacked between blotters withsix blotters separating the sheets. The stack was then pressed forminutes at 150 p.s.i. gauge pressure on a Williams press (manufacturedby the Williams Apparatus Company). The pressed sheets, retained on thecouch blotters, were dried at 260 -280 F. on a steam-heated Noble andWood drier, with the sheet contacting the drum for approximatelytwominutes. After removing the blotters, the dried sheets wereconditioned at 50% relative humidity and 72 F. for a minimum of 24 hoursbefore testing.

The results of tests on papers (handsheets) made from the pulpsidentified in Table V-a are given in Table V-b. The values for the papercharacteristics listed under the various column headings in the lattertable are the results obtained when the respective handsheets are testedusing apparatus and procedures described, for example, in the followingTAPPI Standard Testing Methods:

Test: TA-PPl standard Caliper T411 Tear T414 ts-64 Stretch T457 TensileT404 os-61 Ring crush T472 rn-Sl Mullen T403 ts-63 Brightness T452 m-58Table V-b follows.

than those made from the latter. The digested woods from the TGA-SXScooks also were much easier to refine as compared with those resultingfrom the kraft cooks. The team values for the handsheets made from thepulps of the TGA-SXS cooks are low because the acidity of the treatingliquor was not optimized to obtain optimum tear properties. (As tearvalues increase, tensile values decrease depending upon the refiningtime.) Handsheets made from some of the pulps (e.g., V-E) of the TGA-SXScooks were comparable in tensile and ring crush values with those ofhandsheets from the two kraft cooks.

It is also to be noted that higher temperatures (170 C.) were requiredfor the kraft cooks, in order to obtain the pulps from which handsheetshaving the described properties were obtained, as compared with only 102C. for the TGA-SXS cooks.

EXAMPLE 7 This example illustrates the use of higher temperatures,specifically about 150 C., in the initial digestion ofisopropanol-extracted cypress and black gum chips using a ratio of 100g. of TGA per 100 g. of isopropanolextracted O.D. chips. The liquidreaction medium is a concentrated (about 36%) solution of SXS in aqueous1.8 N PTSA (p-toluenesulfonic acid).

The aqueous PTSA-SXS solutions used are prepared as follows: The SXS isdissolved in the water by stirring with a magnetic stirrer, and to thissolution the PTSA is added with stirring. The TGA is weighed out andadded to about 300 ml, of the PTSA-SXS solution in a graduated cylinder.Additional SXS solution containing PTSA is then added to bring the totalvolume to 1400 ml. This liquor is added to 200 g. of the extracted chipsand cooked in a one-gallon autoclave. The autoclave is brought to atemperature of 150 C. and immediately cooled. The total time ranges fromto minutes.

At the end of the cooking and cooling period, the autoclave is opened,the chips are filtered off, and the clave is rinsed with fresh SXSsolution. The liquor and rinsings are combined, and then diluted withwater in the ratio of 3 parts water to 1 part of the combined liquor andrinsings in order to precipitate the lignin dissolved in the spentliquor.

The chips are placed in 1 liter of 4% aqueous NaOH, stirred for 15minutes, then filtered and washed. The NaOH extract is acidified with18% aqueous HCl to precipitate the lignin. The precipitated lignin isfiltered off. If the lignin is to be analyzed, it is washed thoroughlywith distilled water and air-dried prior to analysis.

The yields of pulp and percentage Klason lignin therein are tabulatedbelow:

Percent PS OF TABLE V-a Dry Ring Bright- Caliper, Tear, Stretch,tensile, crush, Mullen, ness, Pulp No Wood mils g./16 sh. percentlbs/in. lbs. p.s.i. percent; Cypress 7. 2 s3. 0 1. 2 37. 5 57. 5 55. 450 Black gum plus cypress- 8. 4 70. 5 1. 1 35. 5 54. 6 50. 3 53 7. 9104. 9 0. 9 32. 5 59. 4 66. 5 50 7. 7 123. 8 0. 2 47. 2 51. 0 75. 9 457. 4 6. 4 14. 4 48. 4 62. 6 S1. 1 45 V-F -do 9. 2 181 50 62 21 V- G Pine8. 2 53 60 20 1 Ring crush, lbs.=Short column ring crush, lbs.l6-in.circumference. 2 Brightness, percent=Photovolt brightness, percentreflectance.

From a consider-anon of the data given m Tables EXAMPLE 8 V-a andespecially V-b, it will be seen that the pulps of the TGA-SXS cookscontain much less lignin than those made from the two kraft cooks, andthat hand- This example illustrates the use of a differentorganomercaptan, specifically n-butylmercaptan, in a two-stage techniquefor pulping black gum chips in accordance sheets made from the formerpulps are much brighter 75 with the present invention.

The general procedure is essentially the same as in Example 7 with theexception that 50 g. of n-butylmercaptan per 100 g. of 0.1). 'black gumchips is used in a liquid reaction medium containing a concentrated(about 36%) solution of SXS in aqueous 1.8 N PTSA. The digestion iscarried out at atmospheric pressure for 4 hours at a temperature rangingfrom 79 C. to 97 C. The yield of pulp is 49.7%, and the content ofKlason lignin is 8.8%.

EXAMPLE 9 but such control is not always such as to provide three ormore refining points bracketing 55 seconds Williams Slowness.

Other details of the operating conditions for the individual cooks, andthe percentages of pulp yields and Klason lignin contents thereof, aregiven in Table VI which follows. Where is designated in the columnheaded Time, Hrs, it means that the wood chips are heated to thespecified temperature (150 C.), and having reached that temperatureheating of the autoclave is immediately discontinued, and the digestedwood is al lowed to cool to ambient or near-ambient temperature.

Table VI follows.

TABLE VI.-PINE COOKS USING TGA-36% SXS HYDROTROI E AGENT Time, Temp.,Initial Final Percent Percent E. or U. hrs. C. 11+ 1 TGA 2 pH pH yieldL.

Cook N 0.:

1 From para-toluenesultonic acid (PTSA). 2 TGA in grams per 100 grams ofO.D. pine.

3 Unextracted. 4 Extracted.

sure. The. 150. C. cooks-are eifected in an autoclave.

In all cases with the exception ofcook No. 6-E (including 6-E-1), theTGAereacted lignin in the digested chips is extracted by post-treatingthe chips by immersion in a 4% aqueous solution of NaOH having about thesame volume asthe cooking-liquor. This slurry is stirred for one hour atroom temperature, filtered, and the isolated solids washed with' hotwater. The extracted chips are run through a Sprout-Waldron refiner todefiber them. The extract is acidified with concentrated H SO toprecipitate the lignin.

In the case of cook No. 6-E the digested chips are first extracted forminutes at 300F. (followed by cooling to atmospheric pressure over aperiod of minutes) in an autoclave in about the same volume of dioxane(2400 m1.) as that of the initial treating liquor. The cihps arefiltered ofi, washed,fdefibered mechanically, and the yield of pulpdetermined, retaining a sample of the pulp for a Klason lignindetermination. This pulp is then extracted for 1 hour at ambienttemperature in a 4% aqueous solution of NaOH, and the yield and lignincontent again determined. The pulp on which these determinations weremade is identified in Table VI The technique employed in refining thedefibered, digested chips is essentially the same as .that describedunder Example 6 with the exception that the procedure includes pulpswherein aliquots (a minimum of three) 'of 'the experimental pulp, in anamount based on the OD. weight of the wetpulp, are, refined with Waterat 1% consistency for varying periods of time in a Mead LaboratoryRefiner. The degree to which each pulp aliquot is refin'ed,-ashereinbefore described, is controlled;

Table VII shows the Williams Slowness values to which three aliquots ofcertain of the pine cooks listed in Table VI were refined, andproperties of handsheets made from the corresponding pulps obtainedafter refining to the indicated degree. All of these pulps were refinedfor 60, and seconds.

Table VII follows.

TABLE VII.PROPERTIES OF HANDSHEETS MADE FROM TYPICAL PINE COOKS OF TABLEVI AFTER REFINING TO VARYING WILLIAMS SLOWNESS VALUES Properties ofHandsheets Williams Density, Dry Ring Tear, Cook slowness, Caliper,lbs/cu. tensile, crush, g./ 16 sh N 0. sec. in. it. p.s.i. lbs.

6-K-1 23. 1 0. 0111 26. 6 2, 170 48 74 6K2 57. 0 0. 0101 29. 7 2, 586 4977 6-K-3. 404. 0 0. 0084 35. 2 3, 760 49 53 6O1 12. 6 0.0102 36. 2 4,510 118 6O2 46. 9 0. 0090 38. 1 5, 120 88 6O3 101. 2 0. 0065 51. 8 8,380 52 6-R-1 7. 1 0. 0130 25. 0 2, 310 61 The data given in- Tables VIand VII show that pulping of lig'nocellulosic material can beeffectively carried out, using a treating liquor comprised of anorganomercaptan and a hydrotrope agent, under less acidic conditionsthan thoseqemployed in. prior examples; and, also, under slightlyalkaline Cook No. 6-T) or approximately neutral (Cook No. 6-S)conditions. In other words, one

does not need to use the relatively high acid concentraa. much lowerconcentration of acid than was used in prior examples in order toascertain desirable conditions for easy defibration. When the cookingtemperature was increased substantially above 100 C., specifically 150C., it was unnecessary to include additional acid in the treating liquorused in the process in order to obtain a satisfactory pulp.

The data in Table VII on handsheets made for Table VI cooks 6-K, 6-0,6-R and 6-S at three dilferent refining times provide information on thepaper-making qualities of the pulps. Note the extremely hightensilestrength development (8380 p.s.i.) and the very compact, densehandsheets (density =51.8 lbs./cu. ft.) obtained from the pulp (58.7%yield) of cook 6O-3 at 120- seconds refining time. Kraft cooks at 52%yield require a refining time of 160 to 180 seconds in order to obtain apulp from which can be made papers having similar physical propertiesother than in percent brightness, in which latter property such papersare lower than that of papers made from pulps produced by the method ofthis invention.

The data in Table VII further show that a better pulp was obtained fromcook 6-0 (initial pH 3.5, yield 58.7% than from cook 6-K (initial pH2.9, yield 76.7% However, as evidenced by the data on handsheets madefrom pulp 6-R, when the hydrogen-ion concentration is lowered further(i.e., the initial pH value is increased to 5.4), the yield of pulp isincreased to 72%; and, from this pulp, one is able to produce handsheetshaving reasonably good tensile-strength properties and good ringcrushcharacteristics. The data on handsheets made from the pulp of cook 6-Sshow that a further lowering of the hydrogen-ion concentration of thetreating liquor (i.e., the initial pH value is increased to 6.8),provides a pulp at 76.8% yield and which contains 20.5% Klason lignin.Handsheets made from this pulp have a tensile strength equivalent and aring-crush value superior to those obtainable from a kraft process.Pulps such as those of cook 6-S would be valuable in the production ofcorrugating media.

In general, the data presented in Tables VI and VII, especially whencondsidered with that presented in the prior examples, show the extremeflexibility of the process of this invention not only with respect tothe various types of lignocellulosic materials to which the invention isapplicable but also with regard to the simplicity of changing processingconditions so that pulps adaptable for making products having manydifferent end-uses can be produced. For example, cypress, pine or othersoftwoods or any of the various hardwoods, and all from the 20 thedigestion conditions, pulp yields and Klason lignin contents thereof aretabulated below:

TABLE VIII.-HYDROTROPE PULPING OF PINE Time, Initial Final Klason hrs.pH pH Yield lignin The pulps that were produced were w-hollyunsatisfactory. The tensile strengths of handsheets made from the pulpscould not be measured because of the inadequacies of the pulps, whilethe ring-crush values of the sheets were only between 35 and 40.Additionally, the defibered, digested pine was very diflicult to refine.

EXAMPLE 10 Essentially the same procedure is followed as described underExample 7 in pulping isopropanol-extracted black gum and aspen chipswith the exception that the TGA (100 g. per 100 g. of 0D. wood) isdissolved in approximately a 36% solution of SXS in aqueous 0.009 N PTSAinstead of in aqueous 0.9 N PTSA as in Example 7.

The yields of pulp and percentage Klason lignin therein are tabulatedbelow:

Percent Percent Klason yield lignin Black gum pulp 41. 1 4. 25

Aspen pulp 50. 0 4. 56

EXAMPLE 11 This example illustrates the use of a treating liquorcomprised of TGA dissolved in approximately a 36% solution of SXS inaqueous 1% concentrated nitric acid (instead of varying amounts of=PTSA). This liquor is employed in treating unextracted pine chips. Theliquorto-wood ratio is 10:1. The digestion is carried out in a 1-liter,3-necked flask provided with a reflux condenser and a thermometer.Digestion is effected for periods of either 2 or 4 hours. In two of thecooks the TGA is omitted to note the effect thereof. The digested chipsfrom two of the cooks are given no post-extraction treatment. Theremaining cooks (three in number) are extraeted with a 4% aqueoussolution of sodium hydroxide at room temperature as was described underExample 9.

Details of the operating conditions for the individual runs, togetherwith the pulp yields and percentage of Klason lignin in the pulp, aregiven Table IX.

TABLE IX.-PULPING OF UNEXTRAOT86IE USING A TGA-SXS-HNOa-HzO TREATINGNitric Cook Time, Temp., acid, SXS, Percent Percent No. Wood hrs. 0.percent TGA 1 percent yield K.L. Post treatment IX-A--- Pine 4 104 l 10036 56. 4 7. 5 R.T. NaOH extn. IX-B do 2 101 1 36 93. 8 30.2 No ext'n.IX-C do. 2 102 1 90 36 70. 3 21. 3 R.T. NaOH extn. IX-D do 2 102 1 0 3684. 2 33. 7 No extn. IX-E do. 2 102 1 0 36 84.3 32. l R.T. NaOH extn.

1 TGA in grams per grams of O.D. pine.

same forest area, could be used as raw materials in the process of thisinvention if a stand of one type could not support a single operation ofa particular kind.

The unique and unobvious results obtained by using a combination of anorganomercaptan and a hydrotrope agent such as, for example, sodiumxylene sulfonate, will be better appreciated from a consideration of theresults obtained when a 36% aqueuos solution of SXS alone (no TGA orother organomercaptan was present) was similarly used as the treatingliquor in digesting pine chips for 2, 3 and 8 hours at C. Other detailsof 7 contents of EXAMPLE 12 This example illustrates the TGA cooking ofisopropanol-extracted pine chips under at least initially alkalineconditions ranging from 8.6 (cook IO-A) to 12.1 (co k 10-H) atliquor-to-wood ratios of 4.5 :1, and with or without a post-treatment ofthe digested chips with a 1% aqueous solution of sodium hydroxide at 97or 98 C. In other words, the pulping technique is one-stage when no NaOHpost-treatment is applied due to the fact that a large amount of theorganomercaptan-reacted lignin has dissolved in the alkaline solution.In all cooks except one, viz, 10-E cook, NaOH in the amount shown inTable X that follows is added to the treating liquor to provide thealkaline conditions. TGA alone in amounts ranging from 6.4 to 19.3g./100 g. O.D. chips is used in all cooks except 10-I where acombinations of 6.4 g. TGA and 6.05 g. NaSH per 100 g. O.D. chips isemployed. The treating liquor consists essentially of the aforementionedingredients dissolved in a concentrated (about 36%)aq-ueous solution ofSXS. The cooking time is varied from /2 to 3 hours and the cookingtemperature from 150-160 C. 1

Cypress and black gum chips (cooks 10-] and 10K, respectively) arecooked at nearly neutral initial pH values (7.7 and 6.1, respectively).Cypresscook 10-G is digested at an initial pH of the treating liquor of12.5 and a final pH of 12.3.

The general procedure for preparing the treating liquor and for cookingthe'chips is essentially the same as that given under Example '7 withthe exception that a differentratio of liquor-to-wood is employed andcooking is continued atthe maximumtemperatures of 150 r 160 C; for thespecified periods of time.

In Table X are'give n details of theoperating conditions for'the'individual cooks and for. the post-treatment (if employed), pulp yields,and pulp analyses for Klason lignin, sulfur and pentosans.

The amount of TGA employed in the aforementioned cypress cook 10-G is6.4 g./ g. wood. A better pulp is obtained using a higher amount of TGA,specifically 19.3 g. TGA, as evidenced by the following results of testscorresponding to those given above, on pine cook 10C and, in addition,the results of stretch tests. These results are given in the followingTable XII.

TABLE XII Williams Density, Dry Mead refining slowness, lbs/cu. tensile,Tear, Stretch time, sec. see. it. p.s.i. g./16 sh. percent The stretchvalues shown in Table XII are especially significant. These values arecomparable to stretch values of similarly made handsheets produced fromkraft pulps wherein the pulp yield is only 52%.

With further reference to the data in Table X it may also be pointed outthat, at a final pH as low as 9.6 (cooks 10-C and 104D), apost-extraction of the digested wood was not required although only 19.3g. TGA/ 100 g. O.D. wood was used. A comparison of the data on cooks10-H and 10-I (Table X) shows that the inclusion of NaSH (cook 10-I) inthe treating liquor, which also contains TGA and SXS, provides evengreater delignification effect (15.9 vs. 20.4 P.L.) than the use of TGAalone with aqueous SXS.

The method of the present invention provides byproduct lignins havingproperties dilferent from those of other processes including thosewherein an organomercaptan, specifically T GA, is used as a pulpingagent in a non-hydrotropic system, more particularly in an aqueoussolution which is free from SXS or other salt of an organic acid that isemployed to form a conventional hydrotrope agent. This is shown, forexample, by the differences in the Water-solubility of the respectivelignins after hydrolysis.

Tabulated below (Table XIII) is a comparison of-the TABLE X Extractionconditions Pulp yield and analysis i NaOH Cook Time, Temp., G. TGA/100NaOH, Initial Final Time, Temp., Cone, Yield, K.L., S, Pentosans 0. hrs.C. g. chips g. pH pH hrs. C. percent percent percent percent percent a10.T 2 150 6. 4 9. 75 7. 7 4. 8 1 98 1 74. 1 34. 1 10-K l 150 6. 4 9.756. 1 4. 6 1 98 1 70.0 22.8

1 Crude TGA. 3 Cypress cook.

3 Black gum cook.

Mead refining times and the Williams Slowness values, as well as thedensity, tensile strength and tear values of papers (handsheets) madefrom the pulp of cypress cook 10G, and in which pulp the ratio of ligninto carbohydrateis 0.39, are given in Table XI.'

i TABLE XI Williams Density, Dry slowness, lbs/cu. tensile, Tear, sec.ft. p.s.i. g./16 sh.

Mead refining time, sec i 60.. 5 22 1,400 156 120 11 26 2, 500 147 26 293, 200 140 with magnetic stirring for 3 hours at C. The cooled reactionmixture was diluted, in volume, with distilled water by an amount'equalto ten times the weight of the alkaline glycol liquor; then acidified toa pH below 2 with 50% HCl. The acid-insoluble precipitate was col- 23lected in a tared sintered funnel, washed with distilled water and driedin vacuo at 50 C.

Table XIII Percent water-soluble after hydrolysis Lignin from cypresspulped with acidic TGA 54 Lignin from cypress pulped with acidic TGA ina conventional hydrotrope agent, specifically aqueous SXS 68 Lignin fromblack gum pulped with acidic TGA in It will be noted from aconsideration of the data given in Table XIII that the lignins from theMcKee hydrotrope and the kraft processes do not undergo hydrolysis toany great extent while all of the other lignins are hydrolyzed to a highdegree, more particularly from about 2 /2 to about ,4 times as much asthe kraft and the McKee hydrotrope lignins. It is also pointed out thatthe lignins obtained from the woods that had been pulped with acidic TGAin aqueous SXS were more readily hydrolyzed under comparable hydrolysisconditions than were the lignins from the woods pulped with a purelyaqueous system 6r TGA in water, i.e., in the absence of the hydrotropeagent SXS (68% vs. 54% and 70% vs. 66%).

The following additional advantages concerning the process of thepresent invention may be pointed out, and related comments made.

By using a hydrotrope agent, e.g., sodium xylene sulfonate, as acomponent of the treating liquor together with an organomercaptan,lignin is removed from the lignocellulosic material and passes into thetreating liquor almost concurrently with the reaction of theorganomercaptan with the lignin in the lignocellulose. As a result, thedigested wood in chip or other subdivided form is easier to refine thanwhen a hydrotrope agent alone is employed or an organomercaptan alone.In other words, milder conditions can be used in digesting the wood orother lignocellulosic material and in refining the digested chips to apulp having properties comparable to, or better than, those heretoforeobtained by prior processes. It will be understood, of course, by thoseskilled in the art that the amount of lignin that is removed from thewood in the reaction stage, that is, the stage wherein theorganomercaptan reacts with the lignin in the wood, depends upon thetype of wood that is to be digested. Thus, in this reaction stage thesoftwoods give up less lignin than do the hardwoods under the samereaction conditions.

As shown by some of the examples, a simple alkaline extraction was madeprimarily to assure maximum removal of the lignin from the digested woodso that, when analysis of the pulp was made, the correct ratio of ligninto carbohydrate could be determined. If analytical data on the pulps hadnot been desired, one could have refined the digested chips without thealkaline extraction and obtained pulps having practically the sameproperties. However, when an organomercaptan, e.g., TGA, alone isemployed in an aqueous system as the treating liquor under otherwisecomparable digestion conditions, an alkaline extraction of the digestedchips is ordinarily required in order to soften the chips suificientlyfor refining to a pulp having the desired properties.

As in the use of a hydrotrope agent alone (i.e., in the absence of anorganomercaptan in the treating liquor), water can be added tothe usedtreating liquor containing an undesirably high amount of lignin in orderto precipitate the lignin. After separation of the precipitated lignin,e.g., by filtration, the dilute liquor is concentrated for reuse in theprocess. Additional conventional hydrotrope agent (e.g., SBX) orhydrotrope-like agent (e.g., dimethylsulfoxide, dimethylformamide,dimethylacetamide or others, examples of which have been previouslygiven) and/ or an organomercaptan, e.g., TGA, are added as make-up tothe recovered solution, in an amount or amounts as desired or as may berequired in order to bring the treating liquor to substantially itsoriginal composition for reuse in the process.

From the foregoing description it will be seen that the presentinvention provides a method of pulping lignocellulosic material(sometimes designated herein as raw lignocellulosic material) whichincludes the steps of digesting said material with a treating liquorthat includes as essential components (I) at least one lignin-reactiveorganomercaptan, e.g., thioglycolic acid, in an amount corresponding toat least about 5 percent (e.g., from about 5 to about percent) by weightof the oven-dried lignocellulosic material, and (II) a hydrotrope agent;and continuing the said digestion for a period at least sufiicient toconvert the lignocellulosic material to a treated material which atleast initially contains organomercaptan-reacted lignin.

The digestion may be effected under acidic, approximately neutral oralkaline conditions. Acid conditions may be provided by acidifying thetreating liquor with such acids as, for example, an organic sulfonicacid, more particularly a toluenesulfonic acid, and specificallyp-toluenesulfonic acid. Or, one may use as the acidifying agent, organicacids the soluble salts (e.g., alkali-metal salts) of which whendissolved in water constitute the aqueous hydrotrope agent, e.g.,xylenesulfonic acid, cymenesulfonic acid and benzoic acid. Mineral acidsalso may be emp oyed as the acidifying agent, e.g., nitric,hydrochloric, sulfuric or phosphoric acid. Alkaline conditions may beprovided by any base or baseforming substance, e.g., such readilywater-soluble bases as the alkali-metal hydroxides. Preferably sodiumhydroxide is employed.

The method of this invention advantageously includes the initial step oftreating the lignocellulosic material (e.g., wood) with an organicsolvent, e.g., isopropanol, acetone or the like. This pretreatment orpre-extraction step removes extractives (including soluble materialssuch as those which are components of tall oil, and other resinousbodies). The residue is lignin-holocellulose, or more commonlydesignated merely as lignocellulose. The pretreatment just described isnot essential in practicing the present invention and may be omitted ifdesired.

The lignocellulose or lignocellulosic material that is converted into apulp in carrying the instant invention into eifect has sometimes beendesignated herein as raw lignocellulosic materia This terminology is notintended to diiferentiate between (1) lignocellulosiccontaining materialor materials that have been extracted (i.e., given the above-describedpretreatment to remove organic-solvent soluble extractives); and (2)those which are unextracted, that is, have not been given such atreatment but instead are in native or virgin form. In other words, theterm raw lignocellulosic materia in singular or plural form, assometimes used in this specification, includes within its meaning bothunextracted and extracted lignocellulosic material(s) as these latterterms have just been defined.

As has been indicated hereinbefore, the scope of the present inventionincludes the method wherein digestion of the lignocellulosic materialand extraction of the organomercaptan-reacted lignin therefrom iscompleted in either one or two stages.

In a typical two-stage method, digestion of lignocellulosic materialwith a lignin-reactive organomercaptan is initiated and continued underacidic conditions at a'temperature and for a period of time sufiicientto convert the lignocellulosic material to a treated material containingorganomercaptan-reacted lignin. The excess treating liquor is thenremoved (e.g., by drainage from the digestion vessel) from the digestedlignocellulosic material and the latter is washed, e.g., with water and,preferably, hot water. Thereafter the organomercaptan-reacted ligninretained by the washed residue is extracted by contacting the saidresidue with an organic or inorganic extractive agent for the saidlignin. This extractive agent may be a solution of an inorganic base,such as an aqueous solution of sodium or other alkalimetal hydroxideand, more particularly, an aqueous solution of sodium hydroxidecontaining from about 0.5 to about weight percent of NaOH. Or, theextractive agent maybe an extractive amidogen compound such as analkanolamine, and advantageously monoethanolamine. With extractiveagents or solutions thereof boiling below about 200 C., the temperatureof extraction is within the range of, for example, from ambienttemperature to the reflux temperature of the extraction liquor.

The two-stage process herein described is not limited to processeswherein the first or digestion stage is carried out under acidicconditions. It may also be employed, as desired or as may be required,when the digestion is effected at, for example, approximately neutralconditions throughout the digestion period; or approximately neutralinitially and acidic at the end; or under relatively low alkalineconditions (i.e., alkaline pH below about 11.0) which either remainthusly throughout the period of digestion or are approximately neutralor acidic at the end.

In some cases it may not be necessary, in a two-stage process thatincludes a digestion step and an extraction step, to wash the residue(i.e., digested lignocellulosic material) remaining after the excessliquor has been removed therefrom. For example, when the recovery oftreating liquor or of the extractive agent is not unduly complicated bythe elimination of this wash, then said wash may be omitted from theabove-described two-stage technique.

I claim:

1. The method of pulping lignocellulosic material which includes thesteps of (A) digesting said material with a treating liquor thatincludes as essential components (I) at least one lignin-reactiveorganomercaptan in an amount corresponding to at least about 5 percentby weight of the oven-dried lignocellulosic material, and (II) ahydrotrope agent, and (B) continuing the said digestion at a temperatureand for a period of time at least sufiicient to convert thelignocellulosic material to a treated material which at least initiallycontains organomercaptan-reacted lignin.

2. The method as in claim 1 wherein the lignin-reactive organomercaptanincludes thioglycolic acid, and the amount of the organomercaptancorresponds to from about 5 to about 100 percent by Weight of theoven-dried lignocellulosic material.

3. The method as in claim 1 wherein the treating liquor is acidic andcontains an organic sulfonic acid, and the organomercaptan isthioglycolic acid in an amount corresponding to from about 5 to about100 percent by weight of the oven-dried lignocellulosic material.

4. The method as in claim 3 wherein the organic sulfonic acid is atoluenesulfonic acid.

5. The method as in claim 1 wherein the treating liquor is acidic andcontains nitric acid; and the organomercaptan is thioglycolic acid in anamount corresponding to from about 5 to about 100 percent by weight ofthe oven-dried lignocellulosic material.

6. The method as in claim 1 wherein the lignin-reactive organomercaptanincludes n-butylmercaptan, and the 2'6 amount of the organomercaptancorresponds to from about 5 to about percent by weight of the oven-driedlignocellulosic material.

7. The method as in claim 1 wherein the hydrotrope agent is aconcentrated aqueous solution of a soluble salt of an organic acid.

8. The method as in claim 7 wherein the soluble salt of an organic acidis at least one member of the group consisting of the alkali-metal saltsof xylenesulfonic, cymenesulfonic and benz-oic acids.

9. The method as in claim 8 wherein the alkali-metal salt is sodiumxylene sulfonate.

10. The method as in claim 1 wherein the lignocelluosic material ishardwood.

11. The method as in claim 1 wherein the lignocellulosic material issoftwood.

12. The method as in claim 1 wherein digestion is initiated andcontinued under acidic conditions.

13. The method as in claim 1 wherein digestion is initiated andcontinued under approximately neutral condition-s.

14. The method as in claim 1 wherein digestion is initiated andcontinued under alkaline conditions.

15. The method as in claim 1 which includes the initial step of treatingthe lignocellulosic material with an organic solvent to removeorganic-solvent soluble material from the said lignocellulosic material.

16. The method as in claim 15 wherein the organic solvent isisopropanol.

17. The method as in claim 1 wherein digestion of the lignocellulosicmaterial and extraction of organomercaptan-reacted lignin therefrom iscompleted in one stage; the lignin-reactive organomercaptanincludesthioglycolic acid; the amount of the organomercaptan correspondsto from about 5 to about 100 percent by weight of the oven-driedlignocellulosic material; the hydrotrope agent is a con centratedaqueous solution of sodium xylene sulfonate; the digestion is effectedunder alkaline conditions at an initial pH not less than about 11.0; thetemperature of digestion is within the range of from about C. to about200 C.; and the time of digestion is within the range of from about /2to about 8 hours.

18. The method as in claim 17 wherein the lignocellulosic material ispine wood, and the temperature of digestion is Within the range of about160 C.

19. The method as in claim 1 wherein digestion of the lignocellulosicmaterial and extraction of organomercaptan-reacted lignin therefrom iscompleted in two stages; the lignin-reactive organomercaptan includesthioglycolic acid; the amount of the organomercaptan corresponds to fromabout 5 to about 100 percent by weight of the ovendried lignocellulosicmaterial; the hydrotrope agent is a concentrated aqueous solution ofsodium xylene sulfonate; the digestion with the treating liquor isinitiated and continued under acidic conditions at a temperature and fora period of time suflicient to convert the lignocellulosic material to atreated material containing organomercaptan-reacted lignin; and themethod includes the following additional steps:

(C) removing the excess liquor from the material that has been digestedunder acidic conditions with the treating liquor and washing theresidue; and

(D) extracting organomercaptan-reacted lignin retained by the washedresidue by contacting the said residue with an organic or inorganicextractive agent for the said lignin.

20. The method as in claim 19 wherein the treating liquor additionallycontains a toluenesulfonic acid.

21. The method as in claim 19 wherein the agent for extracting theorganomercaptan-reacted lignin is a solution of an inorganic base.

22. The method as in claim 21 wherein the solution is an aqueoussolution of sodium hydroxide containing from about 0.5 to about 5 weightpercent of NaOH.

23. The method as in claim 19 wherein the agent for extracting theorganomercaptan-reacted lignin is an extractive amidogen compound.

24. The method as in claim 23 wherein the extractive amidogen compoundis an alkanolamine.

25. The method as in claim 24 wherein the alkanolamine ismonoethanolamine, and the temperature of extraction is within the rangeof from ambient temperature to the reflux temperature of the extractionliquor.

References Cited Wood Chemistry, Wise & John, 2nd ed., vol. I, pub. byReinhold Pub. Corp., New York, N.Y., 1952, p. 435 and p. 498.

HOWARD R. CAINE, Primary Examiner U.S. C1. X.R.

